Data knitting tandem dispersive range monochromator

ABSTRACT

Aspects of a tandem dispersive range monochromator and data knitting for the monochromator are described herein. In one embodiment, the monochromator includes a tandem diffraction grating, a grating drive motor that rotates the tandem diffraction grating to provide, by diffraction of broadband light, first dispersed wavelengths of light and second dispersed wavelengths of light, a detector that detects a first reflection from the first dispersed wavelengths of light and a second reflection from the second dispersed wavelengths of light, and processing circuitry that knits together data values from the first reflection and data values from the second reflection to provide a spectrum of combined data values. By using a tandem diffraction grating having different dispersive surfaces, measurements of relatively high precision and quality may be taken throughout a wider spectral range, and the measurements may be knitted together to provide a spectrum of combined data values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. Non-provisionalapplication Ser. No. 14/213,214, filed Mar. 14, 2014, which claims thebenefit of U.S. Provisional Application No. 61/792,209, filed Mar. 15,2013, the entire content of both of which are hereby incorporated hereinby reference.

BACKGROUND

Monochromators are optical instruments used to separate monochromaticlight from a wider range of wavelengths of light. To spatially separatecolors or bands of broadband light, a monochromator may rely uponoptical dispersion by way of a prism or diffraction by way of adiffraction grating. Grating monochromators may disperse broadband lightover a certain range of wavelengths, such as ultraviolet, visible, orinfrared, for example, using replica gratings.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the embodiments described herein can be better understoodwith reference to the following drawings. The elements in the drawingsare not necessarily to scale, with emphasis instead being placed uponclearly illustrating the principles of the embodiments. Additionally,certain dimensions or positionings may be exaggerated to help visuallyconvey certain principles. In the drawings, similar reference numeralsbetween figures designate like or corresponding, but not necessarily thesame, elements.

FIG. 1 illustrates an example tandem dispersive range monochromatorincluding a tandem diffraction grating according to an embodimentdescribed herein.

FIG. 2 illustrates the tandem dispersive range monochromator of FIG. 1with a rotated tandem diffraction grating.

FIG. 3 illustrates a perspective view of an example tandem diffractiongrating of the monochromator of FIG. 1 according to an embodimentdescribed herein.

FIG. 4A illustrates a side view of the tandem diffraction grating ofFIG. 3 according to an embodiment described herein.

FIG. 4B illustrates a cutaway side view of the tandem diffractiongrating of FIG. 3 according to an embodiment described herein.

FIG. 5A illustrates an example geometry of a detector and sampling trayof the tandem dispersive range monochromator of FIG. 1 according to anembodiment described herein.

FIG. 5B illustrates a second geometry of the detector and sampling trayof FIG. 5A according to an embodiment described herein.

FIG. 5C illustrates a third geometry of the detector and sampling trayof FIG. 5A according to an embodiment described herein.

FIG. 6A illustrates an example flowchart of a process of tandemdispersive range sample scanning performed by the monochromator of FIG.1 according to an embodiment described herein.

FIG. 6B illustrates an example flowchart of a process of tandemdispersive range sample scanning and knitting performed by themonochromator of FIG. 1 according to another embodiment describedherein.

FIG. 6B illustrates an example flowchart of a process of tandemdispersive range sample scanning and knitting performed by themonochromator of FIG. 1 according to another embodiment describedherein.

FIG. 7 illustrates example data values from a first reflection of firstdispersed wavelengths of light and data values from a second reflectionof second dispersed wavelengths of light.

FIG. 8A illustrates an example of aligning data values from the firstreflection and data values from the second reflection.

FIG. 8B illustrates an example of smoothing data values from the firstreflection and data values from the second reflection.

FIG. 9 illustrates an example spectrum of combined data values providedby the monochromator of FIG. 1 according to another embodiment describedherein.

FIG. 10 illustrates an example schematic block diagram of a processingcircuitry environment which may be employed in the monochromator of FIG.1 according to an embodiment described herein.

DESCRIPTION

Monochromators generally rely upon optical dispersion provided by aprism or a diffraction grating. In this context, it is noted that prismsand diffraction gratings can be used to spatially separate colors intoseparate wavelengths of broadband or white light. A diffraction gratingcomprises an optical element having a periodic structure that separatesand diffracts broadband light into its constituent wavelengthcomponents. The components may be separated in direction afterreflection, based on a spacing of the periodic structure of the grating,for example.

A tandem dispersive range monochromator and certain elements thereof aredescribed herein. The monochromator includes a tandem diffractiongrating and is configured for use over a wide spectral range, such as arange including both the color and near infrared or infrared spectrums.By using a tandem diffraction grating having different dispersivesurfaces, measurements of relatively high precision and quality may betaken throughout a wider spectral range. In this context, a tandem ordoublet diffraction grating that relies upon a single optical train forrelatively high precision and quality spectral measurements isdescribed.

In one embodiment described herein, a tandem dispersive rangemonochromator and data knitting for the monochromator are describedherein. In one embodiment, the monochromator includes a tandemdiffraction grating, a grating drive motor that rotates the tandemdiffraction grating to provide, by diffraction of broadband light, firstdispersed wavelengths of light and second dispersed wavelengths oflight, a detector that detects a first reflection from the firstdispersed wavelengths of light and a second reflection from the seconddispersed wavelengths of light, and processing circuitry that knitstogether data values from the first reflection and data values from thesecond reflection to provide a spectrum of combined data values. Byusing a tandem diffraction grating having different dispersive surfaces,measurements of relatively high precision and quality may be takenthroughout a wider spectral range, and the measurements may be knittedtogether to provide a spectrum of combined data values. In anotheraspect, the processing circuitry controls a sample drive motor to varyan angle of incidence of the dispersed wavelengths of light onto asample for evaluation.

In the following description, a general description of a tandemdispersive range monochromator and its elements is provided, followed bya discussion of the operation of the same.

FIG. 1 illustrates an example tandem dispersive range monochromator 10including a tandem diffraction grating 110 according to an embodimentdescribed herein. The monochromator 10 is enclosed in a housing (notshown), within which one or more platforms or other supporting means arerelied upon to mount and support the elements described herein. Asillustrated, the monochromator 10 includes an enclosure 100 for thetandem diffraction grating assembly 110. The enclosure 100 may beembodied as one or more walls and/or baffles, for example, whichrestrict the entry and/or exit of stray light, but is not limited to anysize, shape, or construction.

Among other elements, the monochromator 10 further includes a lightsource assembly 102, an entrance optics assembly 104, an entrance slitassembly 106, an exit slit assembly 120, an exit optics assembly 122, asample tray 124, a sample tray drive motor 126, a sample tray positionencoder 128, a detector 130, a grating drive motor 140, a gratingposition encoder 142, processing circuitry 150, a display 160, andinput/output (I/O) interfaces 170. As described in further detail below,among other functions, the processing circuitry 150 controls the gratingdrive motor 140 to rotate the tandem diffraction grating 110 overdifferent dispersive side surfaces about a pivot point 116, to dispersebroadband light over a wider range of wavelengths more accurately thanwould be possible with a single dispersive side surface. The processingcircuitry 150 may also knit together data values across first and secondspectrums to provide a spectrum of combined data values and display thespectrum of combined data values on the display 160.

In one embodiment, the light source assembly 102 includes a halogenlight bulb, although any source of broadband light suitable for theapplication may be relied upon among embodiments. The entrance opticsassembly 104 may include optical elements that collimate the broadbandlight, such as one or more spaced-apart expander and/or plano-convexlenses or other elements, without limitation. The entrance slit assembly106 includes a slit though which at least a portion of the broadbandlight 108 may be selectively passed into the enclosure 100. Amongembodiments, the size of the entrance slit may be selected for suitableperformance of the monochromator 10, and the slit may be selectivelycovered and/or uncovered by a sliding shutter (not shown) driven by anoffset solenoid (not shown), for example. Any suitable shutter mechanismmay be used for this purpose. The shuttering operation of the solenoidmay be controlled by the processing circuitry 150, for example, duringvarious operations of the monochromator 10, such as dark scan,calibration (or reference) scan, and live scan operations, for example.

Within the enclosure 100, the tandem diffraction grating 110 is mountedto rotate about the pivot point 116 by way of the grating drive motor140. Thus, the tandem diffraction grating 110 can be rotated under thecontrol of the processing circuitry 150, as described herein. In oneembodiment, the tandem diffraction grating 110 includes a firstultra-violet (UV) to visible (VIS) grating 112 and a secondnear-infrared (NIR) to infrared (IR) grating 114. In other embodiments,the tandem diffraction grating 110 may include more than two dispersivegratings. For example, the tandem diffraction grating 110 may includethree or more dispersive gratings, each selected to disperse aparticular range of wavelengths of light. It is also noted that thetandem diffraction grating 110 may take various forms and/or shapesother than that illustrated in the figures, and the relative positionsof the first UV-VIS and second NIR-IR gratings 112 and 114 may bereversed or otherwise altered.

The diffraction gratings described herein may be embodied as substratesof various sizes with parallel grooves replicated on their surfaces, aswould be appreciated in the art. A diffraction grating, such as thegratings 112 and 114, disperses broadband light 108 by spatiallyseparating it according to wavelength, resulting in first dispersedwavelengths of light 108A and second dispersed wavelengths of light 108C(FIG. 2), respectively. Various methods of manufacture of diffractiongratings are known in the field, and the diffraction gratings describedherein may be manufactured using any known method, such as byreplication from master gratings, interferometric control, holographicgeneration, ion etching, or lithography, for example. Diffractiongratings may also include a coating of reflective material over thegrooves, to reflect light.

In various embodiments, the first and second diffraction gratings 112and 114 may be selected for use over any desired range of wavelengthsand sourced from any manufacturer of diffraction gratings, such asOptometrics Corporation of Littleton, Mass., Grating Works of Acton,Mass., or Richardson Gratings™ of Rochester, N.Y., for example andwithout limitation. One example of a diffraction grating for use withnear IR wavelengths is a Hitachi Holographic Grating with a groovedensity of about 600 grooves per mm, although it should be appreciatedthat the use of other diffraction gratings is within the scope andspirit of the embodiments.

Certain diffraction gratings have specific, blazed efficiency curves.The choice of an optimal efficiency curve for a grating depends on thespecific application. In the context of a monochromator, linearefficiency is usually desired. In other words, the intensity of thediffracted bands of light should be constant across the spectral rangeof light being dispersed. It is noted, however, that the efficiency(e.g., the power or intensity of monochromatic light diffracted relativeto the intensity of the incident light) of a diffraction grating isgenerally not constant as the angle of incident light upon the gratingis varied. In other words, as a diffraction grating is rotated in thepresence of incident light upon its surface, the intensity and/orlinearity of the diffracted bands of light may not be perfectly uniform.This lack of uniformity generally results in some measure of error orincreased signal-to-noise ratio in measurements taken by monochromators.

It should also be appreciated that this variation in the output ofdiffracted bands of light during scanning varies respectively amongdifferent diffraction gratings. In this context, according to certainaspects of the embodiments described herein, variations in the intensityand/or linearity of the diffracted bands of light (and other operatingfactors) for each of the gratings 112 and 114, respectively, iscompensated for (at least in part) by individual control of the rate ofangular velocity or displacement of the gratings 112 and 114. Moreparticularly, the rate of angular velocity or displacement for the firstdiffraction grating 112 of the tandem grating 110 may be different thanthat for the second diffraction grating 114 of the tandem grating 110.

Further, according to aspects of the embodiments described below withreference to FIGS. 4A and 4B, the rate of angular velocity ordisplacement for the first diffraction grating 112 may be different thanthat for the second diffraction grating 114, to take into account anoffset distance between the pivot point 116 of the tandem grating 110,which may be coincident to the surface of the first diffraction grating112, and a surface of the second diffraction grating 114. This varied orvariable angular rate control aspect is unique because conventionaldrive systems generally operate at the same speed over both the UV-VISand NIR-IR spectral regions. The direct and computer controlled drivesystem described herein may be modified for variable scan rates andnumbers of sweeps depending upon signal-to-noise and dispersive gratingspecifications.

Additionally, according to other aspects of the embodiments describedbelow with reference to FIGS. 6B, 7, 8A, 8B, and 9, the variations inthe intensity and/or linearity of the diffracted bands of light (andother operating factors) from the gratings 112 and 114 may becompensated for (at least in part) by knitting data values together.More particularly, the processing circuitry 150 may knit together firstdata values detected by the detector 130 using light from the firstdiffraction grating 112 and second data values detected by the detector130 using light from the second diffraction grating 114, to provide analigned and smoothed spectrum of combined data values for storage and/ordisplay on the display 160.

Referring again to FIG. 1, after being reflected from the firstdiffraction grating 112 of the tandem diffraction grating 110, the exitslit assembly 120 passes a first portion 108B of the first dispersedwavelengths of light 108A out from the enclosure 100. The exit slitassembly 120 may include a physical slit in the enclosure 100 throughwhich the first portion 108B of light may pass. In some embodiments,rather than a physical slit, the exit slit could be an electronic slit,such as a liquid crystal, LCD, or similar device that may be turned offor on to either block or transmit light through a virtual aperture of aparticular shape and size. As another example, a fiber optic may be usedto construct a slit for a specific type of detection system. In effect,any suitable structure may be used for restricting the shape and/or sizeof the dispersed monochromatic light that reaches the detector 130.

The exit optics assembly 122 includes optical elements that collect thefirst portion 108B of light, such as one or more plano-convex collectionlenses, for example, without limitation. In some embodiments, the exitoptics assembly 122 may also include one or more 45° mirrors, etc., tofurther direct the first portion 1088 of light within the monochromator10.

After being collected and/or directed by the exit optics assembly 122,the first portion 108B of the first dispersed wavelengths of light 108Afalls incident upon the sample tray 124 and/or a sample for evaluationin or on the sample tray 124. In turn, the first portion 108B of lightis reflected off the sample and captured by the detector 130. In oneembodiment, the detector 130 is positioned proximate to the sample tray124 and measures the intensity of the light reflected from the sample orthe fraction of radiation absorbed by the sample at specific wavelengths(i.e., the absorbance of the sample). The detector 130 further convertsthe first portion of reflected light to an electrical signal and/or datavalues from which a quantitative analysis of a variety ofcharacteristics of the sample, including constituent analysis, moisturecontent, taste, texture, viscosity, etc., may be determined.

The detector 130 may include one or more lensed assemblies including oneor more image or light sensors that observe the reflection of light fromthe sample at a point of illumination. The field of view of the detector130 may be restricted and the relative geometry and/or placement of theone or more lensed assemblies may be selected to maximize energycollection while minimizing stray light inclusion. To further maximizeenergy collection by the detector 130, in certain embodiments, an ordersorting filter may also be included within the entrance or exit opticsassemblies 104 or 122. Further details regarding the geometry of thedetector 130 and the sample tray 124 are described below with referenceto FIGS. 5A-5C.

The grating drive motor 140 rotates the tandem diffraction grating 110about the pivot point 116. The processing circuitry 150 controls therotational angular velocity and/or acceleration of the tandemdiffraction grating 110 by way of the grating drive motor 140. Becausethe tandem diffraction grating 110 includes two or more diffractiongratings, each having respective optical properties, the processingcircuitry 150 controls the angular velocity and/or acceleration of eachdiffraction grating individually. Among embodiments, the grating drivemotor 140 may be embodied as any suitable permanent magnet stepper motorthat directly drives the rotation of the tandem diffraction grating 110,although other types of motors may be used. For example, variablereluctance motors, brushless DC motors, hybrid stepper motors, or servomotors may be relied upon. Preferably, the grating drive motor 140 isselected to provide a continuous or nearly continuous range of angulardisplacement with good response to control by the processing circuitry150.

The grating position encoder 142 provides feedback on the angularorientation of the tandem diffraction grating 110. For example, thegrating position encoder 142 may provide an encoded signalrepresentative of the absolute angular orientation or position of thetandem diffraction grating 110. This position information is provided tothe processing circuitry 150 as feedback for control of the gratingdrive motor 140. In one embodiment, the grating position encoder 142 maybe selected from among any suitable rotary position encoder having highenough resolution in rotary position for the application. In oneembodiment, an encoder may be selected to yield a 1 in 25,600 incrementof rotation, representative of 0.1 nm of dispersed monochromatic lightfor certain diffraction gratings. The position or increment of rotationmay be interpolated in some embodiments for even greater resolution ofrotary position. One example of such a rotary position encoder is theHEIDENHAIN ERN 480 encoder unit, although other types of encoders may berelied upon among embodiments.

In one aspect, the processing circuitry 150 controls the grating drivemotor 140 to regulate an angular velocity of the tandem diffractiongrating 110 based on an angular orientation of the tandem diffractiongrating 110. In this context, because the angular orientation of thetandem diffraction grating 110 may be used to identify which surface ofthe first and second diffraction gratings 112 and 114 is facing anddispersing the portion of the broadband light 108, the processingcircuitry 150 can control the grating drive motor 140 to regulate anangular velocity of the tandem diffraction grating 110 accordingly. Inanother aspect, the processing circuitry 150 further controls thegrating drive motor 140 to regulate the angular velocity of the tandemdiffraction grating 110 based on the angular orientation of the tandemdiffraction grating 110 and an offset distance between the pivot point116 and a surface of the second diffraction grating 114, as furtherdescribed below.

The sample tray drive motor 126 rotates the sample tray 124 about apivot point. The processing circuitry 150 controls an angle of incidenceof the first portion 108B of light upon the sample tray 124 and/or asample in or on the sample tray 124. The sample tray position encoder128 provides feedback on the angular orientation of the sample tray 124to the processing circuitry 150. Generally, the sample tray positionencoder 128 may be of lower rotary position resolution than that of thegrating position encoder 142. The angular orientation information fromthe sample tray position encoder 128 is provided to the processingcircuitry 150 as feedback for control of the sample tray drive motor126. In one aspect, the processing circuitry 150 controls the sampletray drive motor 126 to adjust an angle of incidence of the firstportion 108B of light upon the sample tray 124, depending upon the typeof measurement being taken by the monochromator 110. Further detailsregarding control of the angle of incidence of the first portion 108B oflight upon the sample tray 124 are described below with reference toFIGS. 5A-5C.

The processing circuitry 150 may be embodied as one or more circuits,processors, processing circuits, or any combination thereof thatmonitors and controls the elements of the monochromator, as describedherein. In this context, the processing circuitry 150 may be configuredto capture, store, and analyze signals and/or data provided by thedetector 130, forward and/or display captured data to another computingdevice or the display 160, receive control feedback from a useroperating the I/O interfaces 170, and store and process various types ofdata. The processing circuitry 150 may also be configured to perform thenecessary calculations and output control signals to elements of themonochromator 150, so as to implement the tandem dispersive range samplescanning process 600A of FIG. 6A and the tandem dispersive range samplescanning and knitting process 600B, as further described below. Further,the processing circuitry 150 may also include driver circuitry forpowering and/or driving the grating drive motor 140 and the sample traydrive motor 126, among other elements which are under computer control.

While a more detailed description of the operation of the monochromator10 is further described below, a brief overview of the operation isdescribed here for additional context before turning to the remainingfigures. In operation, the light source of the light source assembly 102emits a relatively broad spectrum of light or radiation. The entranceoptics assembly 104 collimates the broadband light, and at least aportion of the broadband light is then projected through an entranceslit of the entrance slit assembly 106 and onto the tandem diffractiongrating 112. The tandem diffraction grating 110 provides (i.e.,reflects) first dispersed wavelengths of light 108A by diffraction ofthe portion of the broadband light incident upon it. The tandemdiffraction grating 110 is positioned and rotated over time by thegrating drive motor 140 so that the first portion 108B of the firstdispersed wavelengths of light 108A, which varies or scans over time,passes through an exit slit of the exit slit assembly 120, while theexit assembly 120 blocks other wavelengths of the first light 108A fromexiting the enclosure 100.

The first portion 108B of the first light 108A that passes through theexit slit is determined by the angle of the tandem diffraction grating110, and a spectrum of UV-VIS and NIR-IR light is scanned by rotation ofthe tandem diffraction grating 110 by the grating drive motor 140. Thefirst portion 1088 of the first light 108A that passes through the exitslit is collected by the exit optics assembly 122 and directed incidentonto a sample in the sample tray 124. The detector 130, which issituated proximate to the sample tray 124, measures the intensity ofdiffused, reflected light from the sample and converts the power of thereflected light into an electrical signal and/or data values. Using theelectrical signal and/or data values, a quantitative analysis of thecharacteristics of the sample, such as sample constituents, moisturecontent, taste, texture, viscosity, etc., can be quantitativelydetermined.

Based on the characteristics of the tandem diffraction grating 110, themonochromator 10 provides the dispersion capability of multiplemonochromators in one unit. That is, the monochromator 10 provides thedispersion capability of an ultra-violet to visible spectramonochromator and a near infrared to infrared spectra monochromator, forexample, although additional or other spectral ranges are within thescope and spirit of the embodiments described. As described herein, thetandem grating 110 may be rotated about the pivot point 116 (FIG. 1) tomake use of both sides of the UV-VIS and NIR-IR gratings 112 and 114.

By making use of the tandem diffraction grating 110, the monochromator10 provides accurate dispersion capabilities over non-overlapping (orpartially overlapping) spectra, to achieve wider dispersion than wouldotherwise be possible with a conventional (i.e., non-tandem) grating. Ascompared to a monochromator that includes a single, conventional gratingadapted or manufactured for a relatively wide spectral range ofoperation, the use of the tandem grating 110 provides dispersioncapabilities over at least as wide of a range (e.g., as the conventionalgrating), but with better precision, resolution, and/or granularity. Theseparate gratings allow optimization of linewidths to meet morestringent requirements for linewidth over multiple spectral regions orranges.

Further, making use of the tandem grating 110, reliance upon twoseparate monochromators may be averted. Particularly, the monochromator10 can be relied upon to make relatively high quality spectroscopicmeasurements over the UV-VIS-NIR-IR range of 190 nanometers to 3000nanometers, for example. This results in less overall cost as comparedto using separate monochromators, respectively, for the UV-VIS andNIR-IR ranges, in a smaller footprint. It is noted that using twomonochromators may be cost and/or time prohibitive and results in energyloss for each beam, especially when additional optics must combine thebeams at a sample. Also, using a single conventional grating over thefull UV-VIS-NIR-IR spectral region results in insufficient quality andspectral resolution to make true color (e.g., CIE (InternationalCommission on Illumination) Color Coordinates and L*a*b* Color Spacecertified measurements) and extended range NIR and IR measurements.

Turning to FIG. 2, the tandem dispersive range monochromator 10 of FIG.1 is illustrated with the tandem diffraction grating 110 being rotated.In FIG. 2, the tandem diffraction grating 110 has been rotated so thatthe broadband light 108 is incident upon the surface of the seconddiffraction grating 114, rather than upon the surface of the firstdiffraction grating 112, as in FIG. 1. As illustrated, the seconddiffraction grating 114 disperses the broadband light 108 by spatiallyseparating it according to wavelength, resulting in the second dispersedwavelengths of light 108C. After being reflected from the firstdiffraction grating 114, the exit slit assembly 120 passes a secondportion 108D of the second dispersed wavelengths of light 108C out fromthe enclosure 100.

It should be noted here that, although the diffractive surface of thefirst diffraction grating 112 may be aligned for rotation (i.e.,on-axis) about the pivot point 116, the diffractive surface of thesecond diffraction grating 114 is offset by a distance from the pivotpoint 116 (i.e., off-axis). The processing circuitry 150 takes thisdistance, among other geometric characteristics and/or positions of theelements of the monochromator 10, into account when rotating the tandemdiffraction grating 110. Thus, in various embodiments, one of the UV-VISor NIR-IR gratings is utilized on-axis, and the other one of the UV-VISor NIR-IR gratings is utilized off-axis. If the UV-VIS grating is usedoff-axis, it may be used with a standard shape of grating but specialslewing characteristics specifically adapted for color measurements. Inthis context, some embodiments may rely upon a nominal bandwidth andresulting lineshape of the UV-VIS system to be approximately one-halfthat of the NIR-IR system.

As indicated above, according to aspects described herein, theprocessing circuitry 150 takes into account the spatial relationships(e.g., distances) between the grating surfaces of the first and seconddiffraction gratings 112 and 114 with respect to the entrance slit andthe monochromatic wavelength incident on the exit slit. The processingcircuitry 150 further controls the grating drive motor 140 to regulatethe angular velocity of the tandem diffraction grating 110 based on theangular orientation of the tandem diffraction grating 110 and an offsetdistance between the pivot point 116 and a surface of the seconddiffraction grating 114. In this context, in one embodiment, theprocessing circuitry 150 controls the grating drive motor 140 toregulate a first angular velocity of the tandem diffraction grating 110over a first range of motion for the first diffraction grating 112, andcontrols the grating drive motor 140 to regulate a second angularvelocity of the tandem diffraction grating 110 over a second range ofmotion for the second diffraction grating 114. In other aspects, theprocessing circuitry 150 may knit together first data values detected bythe detector 130 using light from the first diffraction grating 112 andsecond data values detected by the detector 130 using light from thesecond diffraction grating 114, to provide an aligned and smoothedspectrum of combined data values for storage and/or display on thedisplay 160.

FIG. 3 illustrates a perspective view of the tandem diffraction grating110 of the monochromator 10 of FIG. 1 according to an embodimentdescribed herein. The tandem diffraction grating 110 includes a mountingassembly and first and second diffraction gratings 112 and 114. Themounting assembly includes a mount 202A for the first diffractiongrating 112 and a mount 202B for the second diffraction grating 114. Acylindrical (or other suitable shape of) shaft 210 is attached to themounting assembly, as illustrated in FIG. 3. The mounting assembly,including the mounts 202A and 202B for the first and second diffractiongratings 112 and 114, the cylindrical shaft 210, and any otherassociated hardware of the assembly (e.g., screws, bolts, etc.) may beformed from any material suitable for the application, such as stainlesssteel or other metals, for example. Generally, the materials for themounting assembly should be selected so as to minimize flexibility inthe mounting assembly, especially under change in angular acceleration.Such flexibility may translate into variations in the linearity orexpected output of the dispersed wavelengths of light from the tandemdiffraction grating 110. The cylindrical shaft 210 may be anchored atone or more distal ends via upper and/or lower shaft bearings. Theconstruction for the mounting assembly of the tandem diffraction grating110 is generally designed to assure precise, unwavering alignment.

Here, it is noted that the mounting assembly of the tandem diffractiongrating 110 may be relied upon to upgrade or retrofit a monochromatorfor NIR-IR spectral regions to include a diffraction grating for UV-VISspectral regions (or vice versa), by way of the addition of anadditional diffraction grating. In connection with an additionaldetector and/or revised scanning instructions software, as needed, theelements of the instrument may remain the same while expanding theoperating capabilities of the instrument.

Turning to FIGS. 4A and 4B, FIG. 4A illustrates a side view of theexample tandem diffraction grating 110 of FIG. 3, and FIG. 4Billustrates a cutaway side view of the example tandem diffractiongrating 110 of FIG. 3. As illustrated between FIGS. 4A and 4B, themounts 202A and 202B hold and support the first and second diffractiongratings 112 and 114, so that the gratings 112 and 114 can be rotated bythe grating drive motor 130. Also, FIGS. 4A and 4B illustrate that boththe grating drive motor 130 and the grating position encoder 132 arecoupled or attached to the cylindrical shaft 210. Here, as with theexample illustrated in FIG. 3, it should be appreciated that theillustrated shape and dimensions of the tandem diffraction grating 110and the first and second diffraction gratings 112 and 114 are providedby way of example only and not limitation (and may not be representativeof all embodiments).

As can be seen in FIGS. 4A and 4B, centerlines 420A and 420B are drawncoincident to the surfaces of the first and second diffraction gratings112 and 114, respectively. Also, it is noted that the centerline 420A ofthe first diffraction grating 112 is centered at the pivot point 116(FIGS. 1 and 2). In FIGS. 4A and 4B, the distance “A” between thecenterlines 420A and 420B is also illustrated. As outlined above,according to aspects described herein, the processing circuitry 150accounts for the spatial relationships (e.g., distances) between thegrating surfaces of the first and second diffraction gratings 112 and114 (i.e., the distance “A”) with respect to the entrance slit and themonochromatic wavelength incident on the exit slit. The processingcircuitry 150 further controls the grating drive motor 140 to regulatethe angular velocity of the tandem diffraction grating 110 based on theangular orientation of the tandem diffraction grating 110 and the offsetdistance “A” between the centerlines 420A and 420B.

Turning to FIGS. 5A-5C, FIG. 5A illustrates an example geometry of thedetector 130 and sampling tray 124 of the tandem dispersive rangemonochromator 10 of FIG. 1, FIG. 5B illustrates a second example of thegeometry of the detector 130 and sampling tray 124, and FIG. 5Cillustrates a third example of the geometry of the detector 130 andsampling tray 124. At the outset, it is noted that, in FIGS. 5A-5C, thedetector 130 includes separate detectors 130A and 130B. The separatedetectors 130A and 130B may be relied upon, respectively, formeasurements of dispersed light from the first and second tandemdiffraction gratings 112 and 114. In other words, to the extent thatoptical detectors vary in output response or responsivity over a certainwavelength range, the detector 130 may be embodied as separate detectors130A and 130B, each configured for a suitable output response over arelatively narrow wavelength range and corresponding to one of the firstand second tandem diffraction gratings 112 and 114.

As described below, the example geometry of the detector 130 andsampling tray 124 in FIG. 5A may be identified as a 0°/45° geometry, theexample geometry of the detector 130 and sampling tray 124 in FIG. 5Bmay identified as a 45°/0° geometry, and the example geometry of thedetector 130 and sampling tray 124 in FIG. 5C may identified as a22.5°/22.5° geometry. These geometries are defined with reference to theangular difference between the incidence of light upon the sampling tray124 as compared to the normal “N” of the sampling tray 124, and theangular difference between the normal “N” of the sampling tray 124 andthe direction of light reflected into the detector 130.

It is noted that, for some measurements, such as measurements over thecolor or VIS spectrum, for example, the monochromator 10 may rotate theangle of the sampling tray 124 to vary the geometry between the samplingtray 124 and one or more of the detectors 130A or 130B. Thus, to theextent that the angle of incidence of light on a sample impacts theresult of a measurement taken by the monochromator 10, the processingcircuitry 150 may rotate the angular orientation of the sample tray 124by control of the sample tray drive motor 126 to capture variations inthe results. Further, the processing circuitry 150 may determine eithera relative or absolute angular orientation of the sampling tray 124based on feedback from the sample tray position encoder 128.

Referring next to FIGS. 6A and 6B, process flow diagrams illustratingexample processes performed by the monochromator 10 of FIG. 1 areprovided. It should be appreciated that the flowcharts of FIGS. 6A and6B provide merely one example functional arrangement that may beemployed to implement the operations of the monochromator 10, asdescribed herein. In certain aspects, the flowcharts of FIGS. 6A and 6Bmay be viewed as depicting example steps performed by the monochromator10 of FIG. 1. In alternative embodiments, another monochromator or otherinstrument similar to the monochromator 10 may perform the processesillustrated in FIG. 6A or 6B.

FIG. 6A illustrates an example flowchart of a process 600A of tandemdispersive range sample scanning performed by the monochromator 10 ofFIG. 1 according to an embodiment described herein. At reference numeral602, the process 600A includes providing and/or collimating broadbandlight. With reference to the example monochromator of FIG. 1 forcontext, the light may be provided and/or collimated by the light source102 and the entrance optics assembly 104. At reference numeral 604, theprocess 600A includes passing at least a portion of the broadband lightthrough an entrance slit, such as one in the entrance slit assembly 106.

At reference numeral 606, the process 600A includes rotating, by agrating drive motor, a tandem diffraction grating about a pivot point toprovide dispersed wavelengths of light by diffraction of the portion ofthe broadband light. Here, the processing circuitry 150 may rotate thetandem diffraction grating 110 (FIG. 1) using the grating driver motor140 based, in part, on the identification of an angular orientation ofthe tandem diffraction grating 110 using the grating position encoder142 at reference numeral 608. The grating drive motor 140 may becontrolled to regulate an angular velocity of the tandem diffractiongrating 110 based on the angular orientation of the tandem diffractiongrating 110.

The rotating at reference numeral 606 may include controlling therotation by the processing circuitry 150 to regulate the angularvelocity of the tandem diffraction grating 110 based on the angularorientation of the tandem diffraction grating 110 and an offset distancebetween the pivot point 116 and a surface of the second diffractiongrating 112. Additionally or alternatively, the controlling may includecontrolling the grating drive motor 140 to regulate a first angularvelocity of the tandem diffraction grating 110 over a first range ofmotion for the first diffraction grating 112 and to regulate a secondangular velocity of the tandem diffraction grating 110 over a secondrange of motion for the second diffraction grating 114.

At reference numeral 610, the process 600A includes passing at least aportion of the dispersed wavelengths of light though an exit slit in theexit slit assembly 120, for example. At reference numeral 612, theprocess 600A includes controlling, by the sample tray drive motor 126,an angle of incidence of the portion of the dispersed wavelengths oflight onto a sample on the sample tray 124, while controlling thegrating drive motor 140 to regulate the first angular velocity of thetandem diffraction grating 110 over the first range of motion. Thecontrolling at reference numeral 612 may be based, in part, on theidentification of an angular orientation of the sample tray 124 usingthe sample tray position encoder 128 at reference numeral 614.

At reference numeral 616, the process 600A includes detecting thedispersed wavelengths of light and/or a reflection thereof (e.g.,reflection off sample). The detection may be achieved by the detector130, which provides an electrical signal to the processing circuitry 150representative of an intensity, for example, of the dispersedwavelengths of light and/or reflection thereof. The process 600A mayrepeat over time, as needed, so that the monochromator can performvarious measurements, as directed by a user. It is noted that, dependingupon the type of measurement being performed, only one or both halves ofthe tandem diffraction grating 110 may be rotated or oscillated into orabout the path of the broadband light. In other words, the processingcircuitry 150 may be programmed and configured to perform any type ofmeasurement using one or both of the different diffraction gratings ofthe tandem diffraction grating 110, while taking into account theparticular requirements for such measurements.

In other aspects, the process 600A may include one or more blackbackground scans or calibration scans before or after a live scan. Abackground scan may be accomplished with the shutter of the entranceslit assembly 106 closed, and a calibration scan may be accomplishedusing a standard sample.

FIG. 6B illustrates an example flowchart of a process 600B performed bythe monochromator 10 of FIG. 1 according to another embodiment describedherein. In the process 600B, reference numerals 602, 604, 606, 608, 610,612, 614, and 616 include processes similar to those in FIG. 6A. It isnoted that, at reference numeral 616, the process 600B includesdetecting a first reflection (e.g., reflection off a sample) of at leasta portion of first dispersed wavelengths of light and a secondreflection of at least a portion of second dispersed wavelengths oflight. The detection may be achieved by the detector 130, which providesan electrical signal and/or data values representative of an intensity,for example, of the dispersed wavelengths of light and/or the reflectionthereof. Particularly, at reference numeral 616, the detector 130 maydetect a first reflection of at least the portion 108B of the firstdispersed wavelengths of light 108A from the first diffraction grating112 (FIG. 1). The intensity of the first reflection is representative ofthe absorbance of the portion 108B of light 108A by the sample on thesample tray 124. The detector 130 may also detect a second reflection ofat least the portion 108D of the second dispersed wavelengths of light108C from the second diffraction grating 114 (FIG. 2). The intensity ofthe second reflection is representative of the absorbance of the portion108D of light 108C by the sample on the sample tray 124.

Turning to FIG. 7, data values captured by the detector 130 from thefirst reflection, in the UV-VIS spectrum, are plotted on the top frameas the first spectrum 710. Data values captured by the detector 130 fromthe second reflection, in the NIR-IR spectrum, are plotted on the topframe as the second spectrum 720. It should be appreciated that the datavalues in FIG. 7 (and in FIGS. 8A, 8B, and 9) are provided by way ofexample only. As illustrated, at least part of the spectrum 710 overlapswith the spectrum 720.

According to aspects of the embodiments, at reference numeral 618, theprocess 600B includes knitting together data values from the firstreflection (i.e., from the first spectrum 710) and data values from thesecond reflection (i.e., from the second spectrum 720) to provide aspectrum of combined data values. At reference numeral 618, theprocessing circuitry 150 of the monochromator 10 may knit together thespectrum 710 with the spectrum 720, to provide an aligned, smoothed, andcombined spectrum of data values for storage and/or display on thedisplay 160, for example.

In one embodiment, the knitting at reference numeral 618 may includealigning data values from the first reflection with data values from thesecond reflection at reference numeral 618A and smoothing at least aportion of the data values from the first reflection with at least aportion of the data values from the second reflection at referencenumeral 618B.

Turning to FIG. 8A, an example of aligning data values at referencenumeral 618A from the first reflection, spectrum 710, and data valuesfrom the second reflection, spectrum 720, is illustrated. Here, theprocessing circuitry 150 may refer to and compare data values in thespectrum 710 and the spectrum 720 which overlap in spectral range, toidentify a correlation in change among the data values. For example, theprocessing circuitry 150 may identify a similar amount of change betweenin absorbance between individual, consecutive data values for thespectrum 710 and the spectrum 720, across wavelength. In other words,the processing circuitry 150 may identify a similar absorbance envelopeof the spectrum 710 as compared to the spectrum 720, although the datavalues in the envelopes may not be aligned in absorbance value orwavelength position.

Once a correlation in the envelopes of the spectrums 710 and 720 isidentified (at least over the overlapping region of wavelength betweenthem), an amount of absorbance difference (e.g., in the X direction inFIG. 8A) and an amount of wavelength difference (e.g., in the Ydirection in FIG. 8A) between the envelopes may be calculated by theprocessing circuitry 150. The processing circuitry 150 may then alignthe data values in the first spectrum 710 with the data values from thesecond spectrum 720 by subtracting the difference from (or adding thedifference to) one of the two spectrums 710 or 720. Alternatively, eachof the two spectrums 710 or 720 may be adjusted by half the difference.After the aligning at reference numeral 618A, the spectrums 710 and 720may more closely align with each other, as illustrated in FIG. 8B.

After the aligning at reference numeral 618A, the process 600B includessmoothing at reference numeral 618B. At reference numeral 618B, ifmultiple data values exist in the overlapping area 730 (FIG. 8B) of thetwo spectrums 710 or 720, the multiple data values may be smoothed orcombined at reference numeral 618B. For example, if a data value isavailable at a particular wavelength for both the spectrum 710 and thespectrum 720, the two data values may be smoothed or combined byaveraging them. In some embodiments, a mathematical spline or othersmoothing function may be applied across the data values in theoverlapping area 730 after pairs of data values at particularwavelengths have been averaged.

FIG. 9 illustrates an example combined spectrum 910 of combined datavalues provided by the monochromator 10 of FIG. 1. The combined spectrum910 is representative of the combination of the spectrums 710 and 720,using the process of knitting 618 in FIG. 6B and described above. Thecombined spectrum 910 may be provided on a display, such as the display160, for example. By using the tandem grating 110 and knitting togetherthe results captured from light reflected using the first and seconddiffraction gratings 112 and 114, the need for two separatemonochromators may be averted. Particularly, the monochromator 10 can berelied upon to make relatively high quality, combined spectroscopicmeasurements over the UV-VIS-NIR-IR range of 190 nanometers to 3000nanometers, for example. This results in less overall cost as comparedto using separate monochromators, respectively, for the UV-VIS andNIR-IR ranges, in a smaller footprint.

FIG. 10 illustrates an example schematic block diagram of a processingcircuitry environment 1000 which may be employed for the processingcircuitry 150 in the monochromator 10 of FIG. 1 according to anembodiment described herein. The circuitry environment 1000 may beembodied, in part, using one or more elements of a general purposecomputer. The circuitry environment 1000 includes a processor 1010, aRandom Access Memory (RAM) 1020, a Read Only Memory (ROM) 1030, a memorydevice 1040, and an Input Output (“I/O”) interface 1050. The elements ofthe circuitry environment 1000 are communicatively coupled via a localinterface 1002. The elements of the circuitry environment 1000 describedherein are not intended to be limiting in nature, and the circuitryenvironment 1000 may include other elements.

In various embodiments, the processor 1010 may comprise any well-knowngeneral purpose arithmetic processor, programmable logic device, statemachine, or Application Specific Integrated Circuit (ASIC), for example.The processor 1010 may include one or more circuits, one or moremicroprocessors, ASICs, dedicated hardware, or any combination thereof.In certain aspects embodiments, the processor 1010 is configured toexecute one or more software modules. The processor 1010 may furtherinclude memory configured to store instructions and/or code to variousfunctions, as further described herein. In certain embodiments, theprocessor 1010 may comprise a general purpose, state machine, or ASICprocessor, and the processes 600A and 600B described in FIGS. 6A and 6B,respectively, may be implemented or executed by the general purpose,state machine, or ASIC processor according software execution, byfirmware, or a combination of a software execution and firmware.

The RAM and ROM 1020 and 1030 comprise any well-known random access andread only memory devices that store computer-readable instructions to beexecuted by the processor 1010. The memory device 1040 storescomputer-readable instructions thereon that, when executed by theprocessor 1010, direct the processor 1010 to execute various aspects ofthe embodiments described herein.

As a non-limiting example group, the memory device 1040 comprises one ormore of an optical disc, a magnetic disc, a semiconductor memory (i.e.,a semiconductor, floating gate, or similar flash based memory), amagnetic tape memory, a removable memory, combinations thereof, or anyother known memory means for storing computer-readable instructions. TheI/O interface 1050 comprises device input and output interfaces such askeyboard, pointing device, display, communication, and/or otherinterfaces, such as a network interface, for example. The localinterface 1002 electrically and communicatively couples the processor1010, the RAM 1020, the ROM 1030, the memory device 1040, and the I/Ointerface 1050, so that data and instructions may be communicated amongthem.

In certain aspects, the processor 1010 is configured to retrievecomputer-readable instructions and data stored on the memory device1040, the RAM 1020, the ROM 1030, and/or other storage means, and copythe computer-readable instructions to the RAM 1020 or the ROM 1030 forexecution, for example. The processor 1010 is further configured toexecute the computer-readable instructions to implement various aspectsand features of the embodiments described herein. For example, theprocessor 1010 may be adapted or configured to execute the processesdescribed above with reference to FIGS. 6A and 6B.

The flowcharts or processes of FIGS. 6A and 6B are representative ofcertain processes, functionality, and operations of embodimentsdiscussed herein. Each block may represent one or a combination of stepsor executions in a process. Alternatively or additionally, each blockmay represent a module, segment, or portion of code that comprisesprogram instructions to implement the specified logical function(s). Theprogram instructions may be embodied in the form of source code thatcomprises human-readable statements written in a programming language ormachine code that comprises numerical instructions recognizable by asuitable execution system such as the processor 710. The machine codemay be converted from the source code, etc. Further, each block mayrepresent, or be connected with, a circuit or a number of interconnectedcircuits to implement a certain logical function or process step.

Although embodiments have been described herein in detail, thedescriptions are by way of example. The features of the embodimentsdescribed herein are representative and, in alternative embodiments,certain features and elements may be added or omitted. Additionally,modifications to aspects of the embodiments described herein may be madeby those skilled in the art without departing from the spirit and scopeof the present invention defined in the following claims, the scope ofwhich are to be accorded the broadest interpretation so as to encompassmodifications and equivalent structures.

At least the following is claimed:
 1. A monochromator, comprising: atandem diffraction grating including a first diffraction grating, asecond diffraction grating, and a mounting assembly having a rotatableshaft to rotate the tandem diffraction grating; a grating drive motorthat rotates the tandem diffraction grating about a pivot point of therotatable shaft to provide, by diffraction of broadband light, firstdispersed wavelengths of light from the first diffraction grating andsecond dispersed wavelengths of light from the second diffractiongrating; a detector that detects a first reflection of at least aportion of the first dispersed wavelengths of light and a secondreflection of at least a portion of the second dispersed wavelengths oflight; and processing circuitry that knits together data values from thefirst reflection and data values from the second reflection to provide aspectrum of combined data values.
 2. The monochromator of claim 1,wherein the first diffraction grating includes a first periodic surfacestructure for a first range of ultra-violet (UV) to visible (VIS)wavelengths of the broadband light; and the second diffraction gratingincludes a second periodic surface structure for a second range ofnear-infrared (NIR) to infrared (IR) wavelengths of the broadband light.3. The monochromator of claim 1, wherein, to provide the spectrum ofcombined data values, the processing circuitry aligns the data valuesfrom the first reflection with the data values from the secondreflection.
 4. The monochromator of claim 3, wherein the processingcircuitry aligns the data values from the first reflection with the datavalues from the second reflection based on data values which overlap inspectral range among the first reflection and the second reflection. 5.The monochromator of claim 3, wherein, to provide the spectrum ofcombined data values, the processing circuitry further smoothes at leasta portion of the data values from the first reflection with at least aportion of the data values from the second reflection.
 6. Themonochromator of claim 5, wherein the portion of the data values fromthe first reflection and the portion of the data values from the secondreflection overlap in spectral range.
 7. The monochromator of claim 1,further comprising: a sample tray; a sample tray drive motor; and asample position encoder mounted in connection with the sample tray drivemotor that identifies an angular orientation of the sample tray.
 8. Themonochromator of claim 1, wherein the processing circuitry furthercontrols the grating drive motor to regulate an angular velocity of thetandem diffraction grating based on an angular orientation of the tandemdiffraction grating.
 9. The monochromator of claim 4, furthercomprising: a sample tray drive motor, wherein the processing circuitryfurther controls the sample tray drive motor to vary an angle ofincidence of at least one of the first dispersed wavelengths of lightand the second dispersed wavelengths of light onto a sample while theprocessing circuitry controls the grating drive motor to regulate theangular velocity of the tandem diffraction grating.
 10. A method ofscanning, comprising: rotating, by a grating drive motor, a tandemdiffraction grating about a pivot point to provide, by diffraction ofbroadband light, first dispersed wavelengths of light from a firstdiffraction grating and second dispersed wavelengths of light from asecond diffraction grating; detecting, by a detector, a first reflectionof at least a portion of the first dispersed wavelengths of light and asecond reflection of at least a portion of the second dispersedwavelengths of light; and knitting together, with processing circuitry,data values from the first reflection and data values from the secondreflection to provide a spectrum of combined data values.
 11. The methodof claim 10, wherein the tandem diffraction grating comprises: a firstdiffraction grating having a first periodic surface structure for afirst range of ultra-violet (UV) to visible (VIS) wavelengths of thebroadband light; and a second diffraction grating having a secondperiodic surface structure for a second range of near-infrared (NIR) toinfrared (IR) wavelengths of the broadband light.
 12. The method ofclaim 10, wherein the knitting comprises aligning the data values fromthe first reflection with the data values from the second reflection.13. The method of claim 12, wherein the knitting comprises aligning thedata values from the first reflection with the data values from thesecond reflection based on data values which overlap in spectral rangeamong the first reflection and the second reflection.
 14. The method ofclaim 12, wherein the knitting further comprises smoothing at least aportion of the data values from the first reflection with at least aportion of the data values from the second reflection; and the portionof the data values from the first reflection and the portion of the datavalues from the second reflection overlap in spectral range.
 15. Themethod of claim 10, further comprising: Identifying, with a positionencoder, the angular orientation of the tandem diffraction grating overan angular range; and controlling, with processing circuitry, thegrating drive motor to regulate an angular velocity of the tandemdiffraction grating based on the angular orientation of the tandemdiffraction grating.
 16. A monochromator, comprising: a light sourcethat provides broadband light; an entrance optics assembly thatcollimates the broadband light; an entrance slit that passes at least aportion of the broadband light; a tandem diffraction grating including afirst diffraction grating, a second diffraction grating, and a mountingassembly having a rotatable shaft to rotate the tandem diffractiongrating, the first diffraction grating including a first periodicsurface structure, and the second diffraction grating including a secondperiodic surface structure; a grating drive motor that rotates thetandem diffraction grating about a pivot point of the rotatable shaft toprovide, by dispersion from the first diffraction grating and the seconddiffraction grating, first dispersed wavelengths of light and seconddispersed wavelengths of light; a detector that detects a firstreflection of at least a portion of the first dispersed wavelengths oflight and a second reflection of at least a portion of the seconddispersed wavelengths of light; and processing circuitry that knitstogether data values from the first reflection and data values from thesecond reflection to provide a spectrum of combined data values.
 17. Themonochromator of claim 16, wherein, to provide the spectrum of combineddata values, the processing circuitry aligns the data values from thefirst reflection with the data values from the second reflection basedon data values which overlap in spectral range among the firstreflection and the second reflection.
 18. The monochromator of claim 17,wherein, to provide the spectrum of combined data values, the processingcircuitry further smoothes at least a portion of the data values fromthe first reflection with at least a portion of the data values from thesecond reflection.
 19. The monochromator of claim 16, wherein theprocessing circuitry further controls the grating drive motor toregulate an angular velocity of the tandem diffraction grating based onan angular orientation of the tandem diffraction grating.
 20. Themonochromator of claim 16, further comprising: a sample tray that holdsa sample for evaluation; and a sample tray drive motor, wherein theprocessing circuitry further controls the sample tray drive motor tovary an angle of incidence of at least one of the first dispersedwavelengths of light and the second dispersed wavelengths of light ontothe sample.